Conventionally, there has been provided a pin type cage described in JP 2004-245392 A (Patent Literature 1).
This pin type cage includes a first ring, a second ring, a plurality of pins and a plurality of annular bushings.
The first ring has a plurality of through holes, while the second ring a plurality of screw holes. The through holes extend generally along an axial direction of the first ring, and the screw holes extend generally along an axial direction of the second ring. The plurality of through holes are placed so as to be spaced from one another along a circumferential direction of the first ring, and the plurality of screw holes are placed so as to be spaced from one another along a circumferential direction of the second ring.
One end portion of the pin is housed in the through hole of the first ring, while the other end portion of the pin is screwed to the screw hole of the second ring so as to be fixed to the second ring.
The bushings are placed between the through holes of the first ring and one end portion of the pin by press fitting. After the one end portion of the pin is made immovable relative to the first ring by the bushings, welding is applied to make the one end portion of the pin fixed to the first ring.
In the conventional pin type cage shown above, in the working of the through holes, machining variations of about several tens of μm or so occur to the hole diameter, unavoidably. Therefore, in order to realize an interference (more precisely, a desired interference between the through hole and the bushing) that is far smaller than the machining variations, in conventional pin type cages, it is essential to perform selective fitting of the bushing. In this case, the selective fitting of the bushing requires enormous time and labor, so that the selective fitting of the bushing makes an obstacle to mass production.
Further, in the above conventional pin type cage, selection and insertion of a proper-sized bushing is hard to do, and adjustment of the interference is hard to do. Also, it may occur that an erroneously set value of the interference causes large stress to act locally on weld parts of the bushing, which is not a completely rigid material so that the weld parts may be deformed.
Accordingly, an object of the present invention is to provide a pin type cage which makes it possible to simply and inexpensively apply a desired surface pressure to an inner circumferential surface of a through hole of the first ring and to an outer circumferential surface of a pin-through-hole placement portion placed at this through hole, and which is excellent in strength and good at mass production. Another object of the invention is to provide an assembling method for such a pin type cage.